PROJECT SUMMARY The lung epithelium consists of diverse cell types, as the result of embryonic progenitors undergoing a series of precise cell fate decisions. Upon injury, a successful repair needs to restore the proper cell fates. Recapitulation and modulation of in vivo cell fate biology holds promise for cell-based regeneration therapy. Despite such fundamental importance and our accumulating knowledge of cell fate regulators, the epigenetic basis of lung cell fate ? defined in this proposal as chromatin state and its relationship to transcription factor binding ? is largely unknown, but essential for mechanistic understanding of cell fate regulators. Combining mouse genetics, genomics of both purified bulk and single cells, 3D imaging, and human stem cell technology, this proposal will test our central hypothesis that sequential and combinatorial actions of NKX2-1 and Wnt signaling transcription factors control the epigenetic maturation and maintenance of lung epithelial cell types in vivo. The proposal has the following 3 aims. (1) To test whether lung fate maintenance shifts from Wnt-dependent to NKX2-1 self- reinforcing as the lung matures. (2) To test whether NKX2-1 promotes AT1 versus AT2 cell fate as a result of recruitment by YAP/TAZ/TEAD versus CEBPA, respectively. (3) To test whether NKX2-1 primes AT2 cells for AT1 differentiation.